Thousands of people who worked on rescue and recovery following the 2001 9/11 terrorist attacks may be at increased risk of prostate cancer, thyroid cancer, and myeloma, a new study suggests.

Researchers have already found links between 9/11-disaster exposure and increased risks of asthma, stress-related mental health problems, and heart disease in previous studies. Now, officials from the New York City Department of Health and Mental Hygiene are analyzing data from the World Trade Center (WTC) Health Registry to determine possible effects, if any, of the Twin Towers’ collapse on cancer risk.

“Dust, debris, and fumes from the WTC contained known and suspected carcinogens, including polycyclic aromatic hydrocarbons, asbestos, benzene, and dioxins,” the researchers write in their article published in the Journal of the American Medical Association.

“At issue is whether dosages to exposed individuals were sufficient to cause excess malignancies and, if so, whether such excesses are […] detectable at present,” they write.

The researchers focused on nearly 55,700 people, 22,000 of whom were recovery and rescue workers (fire fighters, other first responders, construction workers, transportation workers, sanitation crews, security, and more) and the remainder of whom live in lower Manhattan, near the Towers. So far, the team only analyzed data on health outcomes, including the incidence of 23 different types of cancer, of these people through the end of 2008. While that is a relatively short time period for cancers to emerge, five to seven years after 9/11 the data already suggest that rescue and recovery workers harbor a 43% higher risk of prostate cancer compared to other residents of New York State during that the time, even after the scientists adjusted for age, sex, race, and smoking status. The risks of thyroid cancer and of myeloma (a disease of the blood plasma cells) were more than double that of ordinary New Yorkers. The heightened cancer risk, however, was not found among residents or others who were briefly exposed to the debris in the hours after the terrorist attacks.

“It’s still pretty early in the process,” says senior study author Steven Stellman, the research director for the WTC Health Registry and a professor of clinical epidemiology at the Mailman School of Public Health at Columbia University. “Most cancers, especially solid tumors, take years to develop,” he says.

That means that the full impact of WTC exposure on cancer risk may not be apparent for many years. Although Stellman says that he and his colleagues will continue to monitor the Health Registry participants for cancer diagnoses as well as for several other health outcomes, he declined to speculate on how long it would take for further cancer links, if any, to become apparent.

In the mean time, it’s not entirely clear why prostate cancer, thyroid cancer, and myeloma would be most strongly associated with WTC exposure. Myeloma, which is relatively rare, has been correlated previously with some workplace exposure to hazardous materials. But thyroid cancer has been linked more often to ionizing radiation, a risk factor not thought to be present at the WTC site, Stellman says. And as for prostate cancer, the environmental risk factors remain “elusive,” he says. “There’s no consensus among researchers.” He also acknowledges that the number of cancer cases in the registry is small, and that the data do not include data on other sources of potential exposure other than the Towers that might account for the elevated risk.

That’s why it’s uncertain how the study’s findings might affect the compensation of victims of 9/11; in 2011, President Obama added 50 types of cancer to the list of health conditions for which victims would be compensated with the $2.8 billion set aside in the James Zadroga 9/11 Health and Compensation Act. The inconclusive connection to tumors, however, makes reimbursement for cancer controversial, since some have argued the funds should be allocated to cover treatment for problems more definitively linked to exposure.

Stellman, however, says that the WTC Health Registry exists to study and clarify exactly those questions, and hopefully will continue to build a stronger understanding of how exposure to the World Trade Center attacks may be related to cancer.